A year ago, the Jets run defense was your basic runway. Through six weeks this season only Baltimore and Pittsburgh have been stingier. For the reason why, it’s hard to get around how hard it is get around nose tackle Kris Jenkins.

In 11 years with Pittsburgh, offensive guard Alan Faneca used to be one of those three guys. And he said it’s not all about just Jenkins’ 349-pound girth and grit, but his guile.

“I usually say three things,” said the Jets guard, asked to rate what separates the big tubs of goo in the middle of defensive lines from three-time Pro Bowlers like Jenkins. “Size, how well they use their hands, and quickness.

“If you are a bigger guy and not really quick, I can tee off on you. A quick guy like Jenkins might take one step and I’m going to fall on my face.”

Egg was on the Jets’ faces last spring when they decided to dump Dewayne Robertson, for whom they traded up to the fourth pick in the 2003 draft, to Denver for just a conditional middle rounder.

In 2006, coach Eric Mangini came from New England committed to the 3-4 defense. But the defense didn’t work for the 315-pound Robertson who got shoved around worse than Chris Baker during contract negotiations. Isn’t the definition of coaching putting players in positions where they can succeed?

Jenkins, on the other hand, had succeeded greatly in his first three years in Charlotte, helping the Panthers reach the Super Bowl in 2004. But Charlotte was a sedentary place he never embraced and where he spent most of his injured 2004 and 2005 seasons in his house, drinking and ballooning to 400 pounds.

His father told him to either prepare to play like a Pro Bowler again or not play at all. A healthy Jenkins rebounded last season, just not enough to make the Panthers feel their defense had to be built around him anymore.

Because New York was the place for a guy who loves theater and art, Jenkins convinced recruiters Mangini and Mike Tannenbaum he was in love with the game again. So the Jets traded 2008 third-and-fifth rounders and invested $35 million ($20 million guaranteed) in a guy better and better suited than the one they had taken fourth overall.

“You can run outside and not have to deal with [Jenkins],” said Mangini, preferring to praise the entire defensive effort and not just Jenkins. And of course, Pace, a significant free-agent upgrade and the resurgent outside linebacker Bryan Thomas are guarding the flanks for Jenkins, who is not exactly LT from sideline to sideline.

Though Pace and Thomas are good eggs, the Jets’ improvement starts with oppositions fast becoming chicken to run up the middle.

“The way Kris is playing forces them to use an extra guy on him, not just let the center block him,” Faneca said. “It makes them think more outside gap than inside gap.

“It puts an offensive line in position to possibly rethink some of its core running plays.”

When today’s opponent, the 1-4 Raiders, have to rethink their core running plays, they have to think they can’t win. Oakland is fourth in rushing, tied for 29th in passing, theoretically a good thing for the Jets since they have given up the third most passing yards in the NFL.

The pass coverage has to get better sure, but the numbers might not. Teams throw when they can’t run. That’s how superior defense starts.

“The sky is the limit,” said Jenkins, an interesting way to put it by a guy who makes it all happen by basically staying rooted like a big shade tree.